1. Field of the Invention
This invention relates generally to printing paper for reproduction machines, and more particularly to reams of transparencies for such machines.
2. Description of the Prior Art
Many reproduction machines, including copiers and printers, have the capability of copying the indicia from an original paper to a clear plastic sheet. These plastic sheets are known as transparencies, and are usually used with overhead projection machines as visual aids for lectures, conferences, etc.
A problem that is encountered when copying onto transparencies is that adjacent transparencies in a stack of transparencies tend to stick together. Furthermore, after the transparencies are printed upon, the print from one transparency may transfer to the bottom surface of the transparency above it, degrading the projected image.
To avoid these problems, a stack or ream of transparencies is typically provided with separator sheets interleaved with the transparencies. The separator sheets eliminate the sticking and image transference problems, but have, in the past, required complexities to be added to the reproduction machines to handle the separator sheets.
The foremost problems encountered with separator sheets is how to transport them through the reproduction machines without printing on them and without increasing the cycle time per copy. In the past, the separator sheet associated with a transparency was sent through the paper path after the transparency had been printed upon, and a sensing mechanism was used to differentiate between the transparency and the separator so that the separator would not be printed upon. A problem with this solution, however, is that by sending the transparency and the separator through the paper handling path separately, the cycle time of the reproduction machine was substantially increased. Furthermore, the sensing mechanism which determines whether a transparency or a separator is being transported through the machine increases the complexity and cost of the machine.
Some reproduction machines, such as the Tektronix 4692 ink jet copier, utilize a vacuum transport system for moving the transparencies and the separator sheets along the paper path. In the Tektronix 4692, a transparency is held to a rotating drum by a vacuum, and an ink jet mechanism prints the desired indicia on the rotating transparency. In the past, vacuum transport systems suffered from the same problems as any other transport systems in that cycle time was increased and costly sensors were required when transparencies were being copied.